Game Freezing/Hang

When I am playing, my game will just hang up for no reason.

I can minimize it but still frozen when I open it again and have no choice but to end the program in task manager. (I only minimize when it hangs)

The moment it hangs once. The next hangup will surely be close if I play again after it hangs (happened thrice).

Any idea why its happening? Surely not from ads since I already purchased char slots.

Currently using Samsung Galaxy S3